Shuro Nakajima

Motion control technique for practical use of a leg-wheel robot on unknown outdoor rough terrains

In this paper, we propose a basic control method for the leg-wheel robot moving on unexplored rough terrains. When moving on a rough terrain, the compliance values and the trajectories of legs are set up according to the environment without using external sensors. And the step axis mechanism that we have developed, realizes the stable rolling movement of the robot. The proposed method is evaluated by a walking experiment in an outdoor natural terrain.

RT-Mover: a rough terrain mobile robot with a simple leg-wheel hybrid mechanism

There is a strong demand in many fields for practical robots, such as a porter robot and a personal mobility robot, that can move over rough terrain while carrying a load horizontally. We have developed a robot, called RT-Mover, which shows adequate mobility performance on targeted types of rough terrain. It has four drivable wheels and two leg-like axles but only five active shafts. A strength of this robot is that it realizes both a leg mode and a wheel mode in a simple mechanism. In this paper, the mechanical design concept is discussed. With an emphasis on minimizing the number of drive shafts, a mechanism is designed for a four-wheeled mobile body that is widely used in practical locomotive machinery. Also, strategies for moving on rough terrain are proposed. The kinematics, stability, and control of RT-Mover are also described in detail. Some typical cases of rough terrain for wheel mode and leg mode are selected, and the robot’s ability of locomotion is assessed through simulations and experiments. In each case, the robot is able to move over rough terrain while maintaining the horizontal orientation of its platform.

Concept of a novel four-wheel-type mobile robot for rough terrain, RT-Mover

In many fields employing robots, e.g., wheelchair robots, rescue robots, and construction robots, those which can move on rough terrain are desired. A robot with a simple mechanism and high mobility for all-terrain is discussed in this paper. A novel type of four-wheel-type mobile robot is developed, and its design is discussed from a functional viewpoint. In addition, strategies for moving on rough terrain are introduced, and its fundamental capability of moving on rough terrain is verified through simulations and experiments.

Adaptive Gait for Large Rough Terrain of a Leg-wheel Robot (First Report : Gait Strategy)

A leg-wheel robot with four mechanically separated legs and two wheels is highly mobile and stable on rough terrain. We discuss the strategy for the robot movement over large rough terrain, classifying topographical features into 13 patterns of combined terrain surface. To traverse all classified terrain, we propose three adaptive gaits: (1) Step-up gait in which frontfoot landing is higher than contact with the wheel ground, and the robot raises itself toward frontfoot landing; (2) Step-down gait in which frontfoot landing is lower than contact with the wheel ground, and the robot lowers itself toward frontfoot landing; and (3) Step-over gait in which frontfoot landing is no higher than contact with the wheel ground, but the robot raises itself as high as possible. 1

Improved Gait Algorithm and Mobility Performance of RT-Mover Type Personal Mobility Vehicle

We have developed a personal mobility vehicle (PMV) with four driven wheels that is capable of negotiating obstacles with a leg motion mechanism. When obstacles are encountered, wheels are lifted, moved ahead in a stepping-like motion, and lowered back down, thereby allowing the PMV to advance further. In our previous paper, we discussed the principle of the gait algorithm used by our PMV, in which wheels are utilized as legs to negotiate obstacles. In the original algorithm, when the wheels encountered terrain that might require leg motion to traverse, the system determined whether such motion was applicable and, if it was, orchestrated a series of leg motions. However, there were terrains that could not be negotiated using the original algorithm. In this paper, we propose an improved gait algorithm, in which when the vehicle encounters terrain intractable by leg motion with its current posture, the vehicle changes its posture until it can traverse that terrain. We verified the effectiveness of the improved gait algorithm through a variety of mobility tests with a passenger. In addition, we present numerical data on the range of terrain topologies that could be negotiated by the proposed algorithm.

Development of four-wheel-type mobile robot for rough terrain and verification of its fundamental capability of moving on rough terrain

In many fields employing robots, e.g., wheelchair robots, rescue robots, and construction robots, robots that can move on rough terrains are desired. A robot with a simple mechanism and high mobility for all terrains is discussed in this paper. A four-wheel-type mobile robot is developed, and its design is discussed from a functional viewpoint. Its fundamental capability of moving on rough terrains is verified through simulations and experiments.

Proposal for personal mobility vehicle supported by mobility support system

We propose a personal mobility vehicle (PMV) supported by mobility support system (MSS), which expands the field of activities of PMV. This vehicle, which is called RT-Mover P-type 2, shows adequate mobility performance in urban area. A strength of it is that it realize both a leg mode and a wheel mode in a simple mechanism. In this paper, we introduce a whole system integrated with both PMV and MSS, and evaluate basic mobility performance by itself experimentally.

Adaptive Gait for Large Rough Terrain of a Leg-Wheel Robot (Third Report: Step-Down Gait)

A leg-wheel robot has mechanically separated four legs and two wheels, and it performs high mobility and stability on rough terrains. The adaptive gait for large rough terrains of the leg-wheel robot is composed of three gait strategies. In this paper, the step-down gait, which is one part of the adaptive gait, is described. The point of theflow of the step-down gait is described. When the robot approaches a downward step, a forefoot touches the surface deeply. It forecasts the existence of the downward step by the information on the forefoot’s touch point. After that, the robot does the step edge searching operation. This searching operation is the point for going down the step, since the robot fell under the step if it has walked without knowing the step. When the body goes down the step a little, the load sharing ratio of legs increases so that the load of the body rests upon legs. Therefore, the robot finds the edge of it, and it changes footsteps for preparation of going down the step. After the preparation, it can lower the body from the step supported by all legs and wheels. To lower the body, the following items are needed similar to the case of an upward step: 1. Acquisition of target value of lowering the body. 2. Correspondence to difference between target depth and actual depth. 1

Proposal of a personal mobility vehicle capable of traversing rough terrain

Abstract Purpose: Personal mobility vehicles (PMVs) are now being actively developed. Most PMVs are wheel-driven, a mode of transport notable for its efficiency. However, such vehicles tend to have little mobility over rough terrain. We propose a new type of PMV, a vehicle that traverses relatively smooth terrain by wheel but is capable of negotiating rough terrain by using its wheel mechanisms as legs. Method: The PMV we propose is intended to provide its user with a degree of outdoor mobility in daily urban life, say when going to a neighbourhood shop or simply taking a stroll. We do not consider elevators and other infrastructural elements that should be barrier-free, but rather focus on unimproved terrains that act as barriers to transport; for example, the steps that often act as de facto boundaries around building entrances. Results: We developed a new type of PMV and implemented a new algorithm to realize the capability to move on rough terrain. We experimentally compared the capability of a commercially available PMV and the developed PMV. Conclusions: Through an experiment involving the traversing of a representative terrain and a comparative experiment using a stock PMV, we demonstrated the features of the proposed PMV. Implications for Rehabilitation We developed a single-seat personal mobility vehicle, the RT-Mover PType 3, which is capable of traversing steps and other unimproved terrain often found within an urban environment. RT-Mover PType 3 can handle oblique slopes and other terrain that can be quite difficult to negotiate with a conventional electric wheelchair, thus enabling individuals with impaired mobility to move freely about urban environments. The current vehicle is primarily intended for the active elderly and other individuals in fairly good health, although, through further research and development, we do hope to extend its usefulness to those with substantial mobility impairments.

Adaptive Gait for Large Rough Terrain of a Leg-Wheel Robot (Fourth Report: Step-Over Gait)

A leg-wheel robot has mechanically separated four legs and two wheels, and it performs high mobility and stability on rough terrains. The adaptive gait for large rough terrains of the leg-wheel robot is composed of three gait strategies. In this paper, the step-over gait, which is one part of the adaptive gait, is described. The proposed method is evaluated by simulations and experiments. The point of the flow of the step-over gait is described. When the body reaches an obstacle, it does not come to advance easily. In this case, the robot can not always understand the height of the obstacle, since its forefeet sometimes do not touch it. Therefore, the robot raises its body as possible as it can, and gets over the obstacle. After getting over it, the body is lowered until it touches the ground. The system judges whether the body touches the ground by the information on load sharing ratio of legs. 1